1. Field of the Invention
This invention is a method and accompanying apparatus which allows the determination with great accuracy of the ionic activities of aqueous electrolyte solutions.
2. Description of the Prior Art
The prior art teaches it is old to measure the pressure difference between a solution and a reference liquid to determine the characteristics of the solution. For example, the USSR Pat. No. 505-916--the closest known prior art--discloses two vessels filled with liquid fuels and placed in a thermostat. Taps are employed as valves for each vessel and each vessel is connected to each leg of a single U-shaped mercury pressure gauge or manometer which can read the pressure difference between the vapors of the liquids. In that patent the reference liquid is fuel and has a known vapor pressure. Using this information and the pressure difference reading allows the calculation of the saturation vapor--and hence quality--of the test liquid.
The essential difference between this reference and my invention resides in the fact that the patent can yield results having no better than a 10 percent accuracy and it does not employ aqueous electrolytes as the test liquids or solutions. Contrary to these prior art results, my invention can achieve an accuracy of 0.01 percent in the pressure difference measurement to yield by calculation an accuracy of 0.0008 percent in the ionic activity measurement. It achieves this result by using very accurate measurements of the pressure difference and then uses the known vapor pressure of pure water to very accurately determine the lower vapor pressure for the test solution. Pure water is also used as a standard for calibrating the pressure readings. This determined lower vapor pressure reading can then be used to very accurately arrive at many determinative results. For example, the ionic activity, heat of solution of each electrolyte, construction of the vapor-liquid phase diagram for each binary and multicomponent solution, and the heat of vaporization of water from a given solution.